1. Field of the Invention
The invention relates to machine tools for cutting inside grooves in a hole of a work piece.
2. Background of the Invention
It is often necessary or desirable to create an internal recess or groove within a tube or hole of a machine part. This process is accomplished using a grooving tool attached to a tool holder on a rotary drive. The end of the grooving tool that is placed in the hole has one or more cutting inserts. These cutting inserts are often radially extendable and retractable. This feature allows the tool to be inserted into a hole, then rotated and extended radially to form the groove along the inside surface of the hole.
Extendable inserts are well known in the prior art. U.S. Pat. No. 2,333,935 and U.S. Pat. No. 2,545,443 each shows extendable inserts for internal grooving. Generally, a central rod is moved in an axial direction and has a tapered surface at its end. The tapered surface engages one or more cutting inserts in a wedging action to convert the axial force into a radial force moving the insert into cutting position. The means for moving the central rod is often mechanical, but electrical or hydraulic movement of such a rod is not new to the art. Regardless of the means for effecting movement, an elaborate control system was always required to control the movement of the central rod. This control is necessary because the position of the central rod determines the diameter of a cut that will be made in the wall of the workpiece.
Current grooving tool technology is also limited by how far a tool is able to reach into a workpiece. The reason for this limitation in the art today is that the means of controlling the diameter of the cut must be in close proximity to the cutting insert.
Another problem of the current technology is the inability of an insert to retract after the cut is complete. Chips or debris interfering with the motion or spring failure can cause the insert to not retract. Most grooving tools now employ a spring to directly pull an insert back to a retracted position. A relatively strong spring is required to overcome the force required to pull an insert back into start position. Spring failure can be serious problem. Because the spring is often the only means of retaining the insert in the shank, failure of the spring can lead to the insert being stuck in an extended position and fouling itself in the workpiece.